FORENSIC SCIENCE

3.1

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The frontalis, orbicularis oris, laris oculi, buccinators and zygomaticus are muscles that are responsible for showing facial expressions such as surprise, anger, fear, disgust, amongst other emotions.

The temporalis and the masseter muscle are responsible for chewing movements.

The sterncleidomastoid and trapezius are neck muscles and can be associated with the throat.

3.2

The principal organs that comprise the nervous system are the brain, spinal cord, nerves and ganglia. These organs also consist of various tissues including nerve, blood and connective tissue. All together the organs and various tissues carry out the activities of the nervous system.

The activities of the nervous system can be grouped together as three overlapping functions. The first of these functions is sensory. There are millions of sensory receptors that detect changes which occur on the inside and outside of the body. They monitor things such as temperature, light and sound from the external environment and from the internal environment they detect variations in pressure, PH, carbon dioxide. All of this gathered information is called sensory output which is converted into electrical signals called nerve impulses which are transmitted to the brain. These signals are then brought together to create sensations, to add a memory or to produce thoughts. The decisions that are made each moment based on the sensory input is the second function, integration.

Based on both the sensory and integration functions, the nervous system responds by sending signals to the muscles, causing them to contract, or to glands, causing them to produce secretions. Muscle and glands are called effectors as they cause an effect in response to directions from the nervous system. This provides us with the third function, motor.

The nervous system as a whole is divided into two subdivisions: the central nervous system and the peripheral nervous system.

The brain and spinal cord are the organs of the central nervous system. Because they are so vitally important, the brain and spinal cord, located in the dorsal body cavity, are encased in bone for protection. The brain is in the cranial vault and the spinal cord is in the vertebral canal of the vertebral column. In addition to bone, the central nervous system is surrounded by connective tissue membranes, called meninges and by cerebrospinal fluid.

The brain is divided into the cerebrum, diencephalon, brain stem and cerebellum.

The largest portion of the brain is the cerebrum which is divided into two cerebral hemispheres. The two hemispheres are two separate entities.

The diencephalon is centrally located and is nearly surrounded by the cerebral hemispheres. The thalamus, which makes up about 80% of the diencephalon, consists of two oval masses of grey matter that serve as relay stations for sensory impulses, except for the sense of smell, going to the cerebral cortex.

The cerebellum is the second largest portion of the brain. Three bundles of myelinated nerve fibres, called cerebellar peduncles, form communication pathways between the cerebellum and other parts of the central nervous system.

The spinal cord extends from the base of the skull to the level of the fist lumbar vertebra and like the brain, it is surrounded by bone, meniges and cerebrospinal fluid. The spinal cord is divided into 31 segments and each segment gives rise to a pair of spinal nerves.

The spinal cord as two main functions. The first is serving as a conduction pathway for impulses going to and from the brain. The second is serving as a reflex centre. The reflex arc is the functional unit of the nervous system. Many reflexes are mediated in the spinal cord without going to the higher brain centres as they are responses to stimuli and do not require conscious thought and require more quickly than reactions that require thought process.

The second of the two subdivisions is the peripheral nervous system. The organs that make up this system are the nerves and ganglia. Nerves are bundles of nerve fibres and ganglia are collections of nerve cells outside the central nervous system.

The peripheral nervous system is further divided into a sensory division which transmits impulses from the peripheral organs to the central nervous system and a motor division which transmits impulses from the central nervous system out to the peripheral organs to cause an affect or action.

The peripheral nervous system consists of the nerves that branch out from the brain and spinal cord and it is these nerves that form the communication network between the central nervous system and the body parts. The peripheral nervous system is further subdivided into the somatic nervous system and the autonomic nervous system. The somatic nervous system consists of nerves that go to the skin and muscles and is involved in conscious activities. The autonomic nervous system consists of nerves that connect the central nervous system to the visceral organs such as the heart, stomach, and intestines and mediates unconscious activities.

3.3

There are two major categories of glands in the body. The first are exocrine glands which have ducts that carry their secretory product to a surface. These glands include sweat, sebaceous, mammary glands and the glands that secrete digestive enzymes.

The second are endocrine glands which secrete hormones and these are secreted directly into the blood and then carried throughout the body. There are eights major endocrine glands throughout the body but they are considered to be one system as they have similar functions.

The first major endocrine gland is the pituitary gland. There are two distinct regions in this gland. The first is the anterior lobe which produces several hormones one of which is the growth hormone is a protein and stimulates the growth of bones, muscles and other organs by promoting protein synthesis. The second region of the pituitary gland is the posterior lobe. One of the hormones that can be found here are the antidiuretic hormone which promotes the reabsorption of water by the kidney which results in less water being lost as urine.

The second major endocrine gland is the pineal gland. This gland consists of portions of neurons, neuroglial cells and specialised secretory cells called pinealocytes. The pinealocytes synthesise the hormone melatonin which affects reproductive development and daily physiologic cycles.

The third major endocrine gland is the thyroid gland which is located in the neck. It consists of two lobes one on each side of the trachea. Internally, the gland consists of follicles which produce thyroxine and triiodothyronine homones. These hormones contain iodine. About 95 per cent of the thyroid gland is thyroxine and the remaining 5 per cent is triiodothyronine. Both of these require iodine for their synthesis.

If there is an iodine deficiency the thyroid cannot make sufficient hormone. This stimulates the anterior pituitary to secrete thyroid stimulating hormone which causes the thyroid gland to increase in size in an attempt to produce more hormones. But it cannot produce more hormones as it does not have the necessary raw material, iodine.

The next major endocrine gland is the parathyroid gland. The parathyroid hormone is the most important regulator of blood calcium levels. The hormone is secreted in response to low blood calcium levels, and its effect is to increase those levels.

The next endocrine gland is the adrenal gland which is paired with one gland located near the upper portion of each kidney. Each gland is divided into an outer cortex and an inner medulla.

The adrenal cortex consists of three different regions with each region producing a different group or type of hormones which are chemically steroids. The first region is the outermost region and mineralocorticoids can be found here. The main mineralocorticoid is aldosterone which acts to conserve sodium ions and water in the body. The next is the middle region from which glucocorticoids are secreted. The principal of glucocorticoid is cortisol, which increases blood glucose levels. The third region is the innermost region and the sex hormones are secreted here.

The adrenal medulla develops from neural tissue and secrete two hormones being epinephrine and norepinephrine. These two hormones are secreted in response to stimulation by sympathetic nerves particularly during stressful situations.

The next gland is the pancreas. This gland has an exocrine portion that secretes digestive enzymes that are carried though a duct to the duodenum. The endrocrine portion consists of the pancreatic islets which secrete glucagons and insulin.

The gonads are the primary reproductive organs and they are the testes in the male and ovaries in the female. Although these organs are responsible for producing sperm and ova they also secrete hormones and are considered to be one of the endocrine glands.

The male sex hormones as a group are called androgens. The main androgen is testosterone which is secreted by the testes. A small amount of the hormone is also produced by the adrenal cortex. The steroid hormone is responsible for the growth and

development of the male reproductive structures, the growth and distribution of body hair, increased skeletal and muscular growth and increased male sex drive.

There are two groups of female sex hormones produced in the ovaries. These are oestrogens and progesterone. These steroid hormones contribute to the development and function of the female reproductive organs and sex characteristics.

3.4

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The stomach is an important organ in the digestive system. It is involved in the second phase of digestion. The stomach lies between the oesophagus and the duodenum and also lying behind the stomach is the pancreas.

The pancreas is a gland organ in the digestive and endocrine system. It is both an endocrine gland producing several important hormones an example of one is insulin. The pancreas is also an exocrine gland secreting digestive enzymes that pass to the small intestine.

The duodenum is largely responsible for the breakdown of food in the small intestine using enzymes. It also regulates the rate of emptying of the stomach via hormonal pathways. These cause the gall bladder to release bile and the pancreas to release bicarbonate and digestive enzymes into the duodenum as they are needed.

The pancreatic duct is a duct joining the pancreas to the common bile duct to supply pancreatic juices which aid in digestion.

The common bile duct carried bile from the gall bladder and the liver into the duodenum. The common bile duct is formed by the junction of cystic duct that comes from the gall bladder and the common hepatic duct that comes from the liver.

The function of the gallbladder is to store bile and concentrate. Bile is a digestive liquid continually secreted by the liver. The bile emulsifies fats and neutralises acids in partly digested food. A muscular valve in the common bile duct opens, and the bile flows from the gallbladder into the cystic duct, along the common bile duct, and into the duodenum.

3.5

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The soft palate is the soft tissue constituting the back of the roof of the mouth. It is responsible for closing off the nasal passage during the act of swallowing and also for closing off the airways.

The tonsils are made of soft glandular tissue and are considered part of the immune system. Their main function is to trap bacteria and viruses which you may breathe in.

The uvula keeps food from going the wrong way down the breathing passage when you swallow.

The tongue is used to manipulate food for mastication.
3.6

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The nasal concha protudes into the breathing passage of the nose. It is responsible for forcing inhaled air flow in a steady regular pattern.

The inferior nasal concha is the largest of the concha and is responsible for the majority of airflow direction, humidification and filtering air through the nose.

The middle nasal concha act as buffers to protect the sinuses from coming in direct contact with pressurised nasal airflow. Most inhaled airflow travels between the inferior and middle nasal conchas.

Sphenoid sinuses drain the mucus into the very back part of the nose.

The external nares are through which are enters the nasal cavity. The openings from the nasal cavity into the pharynx are the internal nares.

The nasopharynx is located above the part of the pharynx that food enters. At the base of the nasopharynx are the soft palate and uvula. When swallowing, there is a dangerous possibility: that food will enter into your nasopharynx and nose. This would disrupt severely your breathing. So, when you swallow, the soft palate and uvula point upwards blocking of the nasopharynx so that neither air nor food can pass through it.